The US Senate backed a resolution on Thursday to end US military support for the Saudi-led war in Yemen, defying President Donald Trump with a historic vote that underscored lawmakers' anger over the murder of prominent Saudi journalist Jamal Khashoggi.

The 56-41 vote in the Senate marked the first time either chamber of Congress has passed a motion to withdraw US armed forces from a foreign military engagement under the War Powers Act.

However, despite the historic result, the Senate resolution must clear additional hurdles before it becomes law.

First, the legislation will head to the US House of Representatives, where a Republican-held majority has already promised to hold off on debating the motion until the next session of Congress in the new year.

Speaking after the vote, Democratic Senator Chris Murphy, one of the resolution's co-sponsors, said it "may not get a vote [in the House] by the end of the year".

While the House will be held by Democrats once that new session begins in January, the resolution may see even more changes before passage there.

If the bill manages to get through the House, it will then go to the White House for signing.

However, Donald Trump has vowed to veto the bill, meaning it would go back to the Senate, where only a two-thirds vote can override a presidential veto.

The Senate is unlikely to override a veto, however, since Trump-backed Republicans picked up a handful more Senate seats during the 2018 midterm election.

Historic result

Still, Thursday's vote is the first time US lawmakers took advantage of a provision in the 1973 War Powers Act, which allows any senator to introduce a resolution to withdraw US armed forces from a conflict not authorised by Congress.

If signed into law, it demands within 30 days an end to all US involvement in the Yemen war, which has not received congressional approval.

Saudi Arabia launched the military campaign in Yemen in 2015 to root out the country's Houthi rebels, who had taken over the capital, Sanaa, and ousted the internationally recognised and Saudi-backed government of President Abd Rabbuh Mansour Hadi.

The US military has since provided intelligence sharing and training to the Saudi-led coalition fighting in Yemen, which includes the United Arab Emirates.

The Pentagon had also been conducting air-to-air refuelling for coalition aircraft, but in November they said they would stop.

Trump's administration pushed hard against the Senate's Yemen resolution by sending US Secretary of State Mike Pompeo and Secretary of Defence James Mattis in late November to brief senators on the US's relationship with Saudi Arabia.

The senior officials insisted that Washington must maintain its support for the Saudi-led coalition and described Riyadh as a key US ally in the region.

Not only was the war in Yemen never authorized by the elected representatives of the American people – it is a humanitarian disaster. An estimated 85,000 children have already died of malnutrition. And in a country of 28 million, nearly half are facing famine. pic.twitter.com/WsWq9h2ZmC

That plan appears to have failed, as politicians from both major US parties have expressed anger over the Trump administration's continued support for Saudi Arabia despite the situation in Yemen, as well as global outrage over the murder of journalist Jamal Khashoggi.

In fact, the Khashoggi case has led several Republicans to break away from the president over his vow to stand by Saudi Crown Prince Mohammed bin Salman, known as MBS.

A Saudi government critic and Washington Post columnist, Khashoggi was murdered inside his country's consulate in Istanbul on 2 October.

The Khashoggi case has shone a spotlight on the devastating impact of the war in Yemen. Tens of thousands of people have been killed since the conflict began, while as many as 14 million people are on the brink of famine, the UN recently warned.